1. Field of the Invention
The present invention relates to an orthotic insert, and more particularly for such an insert which is particularly adapted to function effectively throughout the gait cycle experienced in vigorous running in a forward direction.
2. Background Art
An orthotic insert can be either soft or hard. A hard insert is a substantially rigid member, desirably having a relatively thin vertical thickness dimension and extending from the calcaneus area of the foot (the heel portion) to at least the metatarsal head area of the foot (i.e. that area at the "ball" of the foot). In general, the purpose of a rigid orthotic (sometimes called a functional orthotic) is to first position, and then to control the movements of, the midtarsal and subtalar joints during the gait cycle which the body goes through in walking and running, and also possibly for other movements.
It is believed that a clearer understanding of the background of the present invention will be achieved by first discussing generally: (a) the main components or parts of the human leg and foot and how these function relative to one another; (b) the gait cycle which a person goes through in a normal walking motion; (c) the gait cycle which the person goes through in vigorous running; and (d) the intended function of a rigid orthotic in optimizing the coordinated operation of the person's foot and leg throughout the gait cycle.
For convenience, these various topics will be discussed under appropriate subheadings.
(a) The Main Components or Parts of the Human Leg and Foot and How These Function Relative to One Another
With reference to FIGS. 1-3, there is shown a typical human foot 10, and (in FIGS. 2 and 3) the lower part 12 of the leg 14. The two lower bones of the leg 14 are the tibia 16 and the fibula 18. Below the tibia 16 and fibula 18, there is the talus 20 (i.e. the "ankle bone"). Positioned below and rearwardly of the talus 20 is the calcaneus 22 (i.e. the heel bone). Positioned moderately below and forward of the talus 20 are the navicular 24 and the cuboid 26. Extending forwardly from the navicular 24 are the three cuneform bones 28. Extending forwardly from the cuneform bones 28 and from the cuboid 26 are the five metatarsals 30. Forwardly of the metatarsals 30 are the phalanges 32 which make up the five toes 34.
The movement of the talus 20 relative to the tibia 16 and fibula 18 is such that it enables the entire foot to be articulated upwardly and downwardly (in the motion of raising or lowering the forward part of the foot) and also to permit the entire foot 10 to be moved from side to side. However, the talus 20 is connected to the tibia 16 and fibula 18 in such a way that when the entire leg 14 rotated about its vertical axis (i.e. the axis extending the length of the leg), the talus 20 rotates with the leg 14.
With regard to the relationship of the talus 20 to the calcaneus 22, these move relative to one another about what is called the "subtalar joint" indicated at 36. The subtalar joint 36 can be described generally as a hinge joint about which the talus 20 and calcaneus 22 articulate relative to one another. The hinge axis extends upwardly and forwardly at an angle of about 42.degree. from the horizontal, and also slants forwardly and inwardly at a moderate angle (e.g. about 16.degree. from a straightforward direction).
To explain further the hinge motion of the subtalar joint 36, reference is now made to FIGS. 4a and 4b. The talus 20 can be considered as a vertical board 40, and the calcaneus 22 as a horizontally extending board 42, these being hinge connected to one another along a diagonal hinge line 44, with this hinge line corresponding to the subtalar joint 36. It can be seen with reference to FIG. 4a that as the talus 20 is rotated inwardly about its vertical axis (i.e. the front part of the leg being rotated toward the center of the person's body), there is a corresponding rotation of the calcaneus 22 (i.e. the horizontal board 42) about a horizontal axis. It can be seen in FIG. 4b that an opposite (i.e. outward) rotation of the talus 20 (i.e. the vertical board 40) causes a corresponding rotation of the calcaneus 22 (i.e. the horizontal board 42) in the opposite direction to that shown in FIG. 4a.
This motion described with reference to FIGS. 4a and 4b above is critical in the gait cycle (i.e. the cycle through which the person goes in normal walking or running motion), and this will be discussed more fully below.
With regard to the midtarsal joint 38, this is in reality composed of two separate joints, the talo-navicular and the calcaneal-cuboid. It is a complex joint, and no attempt will be made to illustrate or recreate its motion accurately. Instead, there will be presented a somewhat simplified explanation of its function as it relates to the present invention.
The main concern, relative to the midtarsal joint, is not the precise relative motion of the parts of the foot that make up this joint, but rather the locking and unlocking mechanism of the midtarsal joint which occurs when there is an outward motion of the leg 14 and the talus 20 (outward motion meaning the rotation of the leg 14 and foot 10 about the vertical axis of the leg 14 in a manner that the knee moves outwardly from the person's body), and an opposite inward motion, respectively. When the leg 14 rotates inwardly, the midtarsal joint 38 unlocks so that the portion of the foot 10 forwardly of the joint 38 (i.e. the midfoot 45) is flexible, this being the "pronated" position of the foot. On the other hand, when the leg 14 and talus 20 rotate outwardly, the foot is said to be "supinated" so that the midtarsal joint 38 is locked and the midfoot 45 essentially becomes a part of a rigid lever. In actuality, the midfoot 45 never becomes totally rigid, so that even in the totally supinated position, there is some degree of flexibility in the midfoot 45.
This function of the midtarsal joint will now be explained relative to FIGS. 5a and 5b. It can be seen that FIGS. 5a-b are generally the same as FIGS. 4a-b, except that a forward board member 46 is shown to represent the midfoot 45, this member 46 having a downward taper in a forward direction, and also a lower horizontal plate portion 48. This plate portion 48 is intended to represent that the plantar surface (i.e. the lower support surface) of the midfoot 45 engages the underlying support surface in a manner so as to remain generally horizontal to the support surface.
It can be seen that when the two board members 40 and 42 are in the pronated position of FIG. 5a, the metatarsal joint represented at 50 in FIGS. 5a-b is in a first position which will be presumed to be an unlocked position. In the unlocked position of FIG. 5a, the member 46 is not rigid with the horizontal member 42, and the forward member 46 can flex upwardly relative to the horizontal member 42. (This is the pronated position of the foot 10.) However, in the position of FIG. 5b, the board members 46 and 42 will be presumed to be locked to one another so that the members 42 and 46 form a unitary lever. For ease of illustration, no attempt has been made to illustrate physically the unlocking relationship of FIG. 5a and the locking relationship of FIG. 5b. Rather, the illustrations of FIGS. 5a-b are to show the relative movement of these components, and the locking and unlocking mechanism is presumed to exist.
(b) The Gate Cycle Which the Person Goes Through in a Normal Walking Motion
Reference is first made to FIGS. 6a and 6b. As illustrated in the graph of FIG. 6a, during the normal walking motion, the hip (i.e. the pelvis) moves on a transverse plane, and this movement in the gait cycle is illustrate in FIG. 6b. Also, the femur (i.e. the leg bone between the knee joint and the hip) and the tibia rotate about an axis parallel to the length of the person's leg. (It is this rotation of the leg about its vertical axis which in large part causes the pronating and supinating of the foot during the gait cycle, and this will be explained in more detail below.)
There is also the flexing and extension of the knee, as illustrated in the five figures immediately below the graph of FIG. 6a. Further, there is the flexing and extension of the ankle joint. At the beginning of the gait cycle, the heel of the forwardly positioned leg strikes the ground, after which the forward part of the foot rotates downwardly into ground engagement. After the leg continues through its walking motion to extend rearwardly during the gait cycle, the person pushes off from the ball of the foot as the other leg comes into ground engagement.
The motions described above are in large part generally apparent to a relatively casual observation of a person walking. However, the motion which is generally overlooked by those not familiar with the gait cycle is the inward and outward rotation of the leg about its lengthwise axis to cause the pronating and supinating of the foot through the gait cycle. This will be described relative to FIG. 7a and FIG. 7b.
When the leg is swung forwardly and makes initial ground contact, at the moment of ground contact the leg is rotated moderately to the outside (i.e. the knee of the leg is at a more outward position away from the centerline of the body) so that the foot is more toward the supinated position (i.e. closer to the position shown in FIG. 4b). However, as the person moves further through the gait cycle toward the 25% position shown in FIG. 7a, the leg rotates about its vertical axis in an inside direction so that the subtalar joint is pronating. The effect of this is to rotate the heel of the foot so that the point of pressure or contact moves from an outside rear heel location (shown at 52 in FIG. 7b) toward a location indicated at 54 in FIG. 7b. This pronating of the subtalar joint 36 produces a degree of relaxation of the midtarsal joint 38 and subsequent relaxation of the other stabilization mechanisms within the arch of the foot. This reduces the potential shock that would otherwise be imparted to the foot by the forward part of the foot making ground contact.
With further movement from the 25% to the 75% position, the leg rotates in an opposite direction (i.e. to the outside) so that the midtarsal joint 38 becomes supinated at the 75% location of FIG. 7a. This locks the midtarsal joint 38 so that the person is then able to operate his or her foot as a rigid lever so as to raise up onto the ball of the foot and push off as the other leg moves into ground contact at a more forward location.
With reference again to FIG. 7b, the initial pressure at ground contact is at 52 and moves laterally across the heel to the location at 54. Thereafter, the pressure center moves rather quickly along the broken line indicated at 56 toward the ball of the foot. As the person pushes off from the ball of the foot and then to some extent from the toes of the foot, the center of pressure moves to the location at 58.
(c) The Gait Cycle Which the Person Goes Through In Vigorous Running
The gait cycle which the person goes through in vigorous running is in some respects the same as the gait cycle for walking. However, there is a "floating" period where both of the person's feet are off the ground. Further, the length of time which the foot is on the ground is substantially shorter. For example, in the normal walking gate cycle, where the person is walking at 120 steps per minute, the foot may be on the ground for as long as 0.6 seconds. However, in running, this period of ground contact may be as short as 0.2 seconds.
Also, the force exerted by the foot against the ground can be substantially greater than experienced by the walking gate cycle. These forces could go up to as high as, or greater than, three times the person's body weight.
Another consideration is that for some runners, the heel strike is absent. Rather, the runner's foot will engage the ground surface generally at the outside middle portion of the person's foot, and the center of force or pressure will move in a pattern inwardly toward the centerline of the foot and forwardly as the person pushes off from that foot.
Overall, the stress placed on the foot would be greater than for the gait cycle of normal walking.
(d) The Intended Function of the Orthotic to Improve Operation of the Person's Foot and Leg Throughout the Gate Cycle
If the person's foot were perfectly formed, then there would be no need for an orthotic device. However, the feet of most people deviate from the ideal. Accordingly, the function of the orthotic is first to position the plantar surface of the calcaneus 22 and the midfoot 45 so that the subtalar and midtarsal joints 36 and 38 are initially positioned properly, and to thus control the subsequent motion of the foot parts or components that make up these joints so that the movements of the hip, leg and foot throughout the gait cycle are properly accomplished. It can be readily understood that if the components of the foot have the proper initial position and movement about the subtalar and midtarsal joints 36 and 38, the entire gait cycle, all the way from the coordinated rotation of the hips through the flexing and rotation of the leg, and also through the initial strike of the heel on the ground to the final push off from the toe of the foot, is properly coordinated and balanced for optimum movement.
Since shoes are generally manufactured on a mass production basis, the supporting surface of the interior of the shoe may or may not optimally locate the plantar surface of the foot. Accordingly, it has for many years been a practice to provide an orthotic insert which fits within the shoe to optimize the locations of the foot components. In general, these inserts have been made of various materials, some of which are formed as laminated structures to provide a relatively rigid support for the heel and midfoot regions of the foot.
These orthotics can be formed in a variety of ways. A preferred method of forming an orthotic insert is described in the applicant's U.S. Pat. No. 3,995,002. In that method, there is formed a negative mold or slipper cast from which a positive cast of the plantar surface of the individual's foot is formed. Using this positive cast as a template, an orthotic insert is formed to underlie an area under the foot. The insert itself is fabricated by applying to the positive cast the material which is to orthotic insert. The precise configuration of the insert will depend upon the prescribed corrective measures to be taken for the individual's foot.